Power mosfet transistor circuit

Abstract

The present invention relates to a power MOS transistor having a current limiting circuit incorporated in the same substrate as the transistor. The power MOS transistor includes a drain region extending through the substrate between opposed first and second surfaces, a plurality of body regions in the substrate at the first surface, a separate source region in the substrate at the first surface within each body region and a channel extending across each body region between its junction with its respective source region and its junction with the drain region. A conductive gate is over and insulated from the first surface and extends over the channel regions. A first conductive electrode extends over and is insulated from the gate and contacts a first portion of the source regions. A second conductive electrode extends over and is insulated from the gate and contacts a second portion of the source regions. The second portion contains a smaller number of the source regions than the first portion. The current limiting circuit includes a bipolar transistor formed in a well region in the substrate, a zener diode formed in a second well region in the substrate and two resistors formed over and insulated from the first surface. The current limiting circuit is connected between the second portion of the source regions and the gate so as to reduce the power through the circuit.